Apparatus for extruding hollow plastic articles



July 25, 1967 PARK 3,332,112

APPARATUS FOR EXTRUDING HOLLOW PLASTIC ARTICLES Original Filed Feb. 25,1963 5 Sheets-Sheet l INVENTOR Amara par/r ATTORNEYS July 25, 1967 R. H.PARK 3,332,112

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APPARATUS FOR EXTRUDING HOLLOW PLASTIC ARTICLES Original Filed Feb. 25,1963 5 Sheets-Sheet .3

INVENTOR Roberf H. Par/f BY %AM ATTORNEYS l '11 |l I82 /79 :li'll ma i-178 II I! I L I? I (A |'I United States Patent 3,332,112 APPARATUS FOREXTRUDIN G HOLLOW PLASTIC ARTICLES Robert H. Park, Dennis, Mass.,assignor to Brockway Glass Company, Inc., Brockway, Pa. Continuation ofapplication Ser. No. 260,715, Feb. 25, 1963. This application July 6,1965, Ser. No. 473,892 The portion of the term of the patent subsequentto Feb. 26, 1980, has been disclaimed 7 Claims. (Cl. 1S14) Thisinvention relates to an apparatus for producing hollow plastic articles,such as containers, by extruding a tubular blank and subsequentlyblowing the same outwardly into conformity with a mold. This applicationis a continuation of my copending application, Ser. No. 260,715 filedFeb. 25, 1963, and now abandoned, which in turn is acontinuation-in-part of my patent application, Ser. No. 775,055, filedNov. 19, 1958, now Patent No. 3,078,507, dated Feb. 26, 1963.

According to the apparatus of the aforesaid patent a tubular blank orparison is extruded through an extrusion orifice, which is a figure ofrevolution, and which converges round the axis of extrusion, and aboutan extrusion mandrel comprising a plurality of concentric tubularelements having generally tapering ends, which elements are adapted tobe moved independently and cyclically during and subsequent to theextrusion process.

In producing blown plastic containers, for instance, wherein the body isfiat or oval, it is desirable in order to form a body having uniformwall thickness after blowing, to extrude a tube wherein the wall isthicker at some points than at others.

In the aforesaid patent means are provided for cyclically moving theconcentric tubular members axially to vary the physical characteristicsof the extruded tube along its length. More particularly, means areprovided for producing tubular extrusions wherein selected portionsalong the length of the extrusion have non-uniform wall thicknesses,considered circumferentially. In the aforesaid patent this variableextrusion is accomplished by employing plural axially movable sleevemembers having tapered ends and with the tapered end of at least one ofsaid sleeves of non-circular form.

In one form of the apparatus of the present invention an equivalentresult is attained byv employing internal cyclically movable extrusionmembers which are figures of revolution and an external extrusion memberhaving portions thereof adjacent at least one sleeve end which arenon-circular whereby a portion of at least one of the cyclicallyvariable extrusion passages employed in extruding a portion of thetubular parison is of varying thickness around the circumference.

By thus scalloping the orifice or the external extrusion surfaceadjacent to the orifice the cost of manufacturing specially shaped partsis reduced, particularly when adapted to the production of specificblown objects. Furthermore, removal and replacement of the cap member isall that is required to vary the range of the dimensionalcharacteristics of the extruded tube.

This ready removal and replacement of the cap member is particularlyadvantageous since the degree of scalloping or non-circularity of theextrusion surfaces must be determined empirically, in fact by cut andtry methods, in producing a tubular parison to suit a particular blownbody shape. To some extent also the extrusion wall thicknesses, orrather the variations therein, are governed by the kind of plasticemployed.

In addition to the above, the present invention also provides novelmeans for facilitating the formation of a satisfactory terminal neckportion of an extruded and blown plastic article. The problems incidentto this objective are particularly present when the blown article isprovided with a false finish, that is, an additional reduced outer neckportion which is removed in trimming the neck portion proper from theultimate blown article.

In the apparatus of the aforesaid patent a degating sleeve isillustrated which in addition to severing the extrusion from the parentbody of plastic material can be used to compress the material in theneck portion of the mold. When such a degating sleeve is not beingemployed to produce such compression or is not present in the apparatus,for instance, the problem of insuring a fully molded false finish isaggravated.

In the present apparatus, by way of example, the false finish is moldedbetween external molding surfaces of the separable mold parts and aninternal mandrel, which may comprise a blow tube as in the presentapparatus. If the extruded material surrounding the blow tube isinsufficient the false finish may be blown out against the mold surfacesleaving an air space around the blow tube. In this event, air will tendto leak between the plastic and the blow tube thereby causing loss ofair and genearlly un desirable extrusion conditions because of thecooling effect of the escaping air on the orifice.

If the wall thickness of the extrusion surrounding the blow tube isexcessive fins are formed which prevent proper closing of the moldparts, causing a very objectionable flash or seam line around the moldedarticle due to incomplete closure of the mold parts. In some cases thefins thus formed may project from the false finish to a degree whichimpedes handling of the article in T ziuipment for subsequent trimmingoperations and the In the present apparatus this problem is avoided byproviding narrow relief areas adjacent to the false finish portion ofthe mold on at least one of the mold parts so that excess plasticmaterial, upon closure of the mold parts, can flow into the relief areaand form fins of controlled thickness which are narrow enough not toimpede trimming operations and which have no tendency to prevent properclosure of the mold parts.

In this way a substantial tolerance in the wall thickness of theextrusion or that part of the extrusion which forms the false finish ispermitted. The wall thickness of the extrusion will be at least as thickas the annular space between the false finish mold and the blow tube andmay be of greater thickness up to the capacity of the aforesaid recessesfor receiving excess plastic material.

While certain representative embodiments of the principles of thepresent invention are illustrated in the draw ings and described in thefollowing specification, it is to be understood that such embodimentsare by way of example only and that the scope of the present inventionis not limited otherwise than as defined in the appended claims.

In the drawings:

FIG. 1 is a general elevational view of one form of the extrusion andblow molding apparatus of the present invention;

FIG. 2 is a view similar to FIG. 1 but taken at right angles thereto;

FIG. 3 is a substantially enlarged cross-sectional view taken similarlyto FIG. 1 showing the extrusion passage portion of the apparatus;

FIG. 4 is a view similar to FIG. 3 with the parts in position for finalextrusion;

FIG. 5 is a View similar to FIG. 3 but showing an embodiment wherein thescalloping is located on the orifice instead of on the internal controlsleeve;

FIG. 6 is a fragmentary elevational view taken similarly to FIG. 2 buton a considerably enlarged scale showing the neck and false finishportion of one of the mold parts;

FIG. 7 is a plan view of the structure of FIG. 6;

FIG. 8 is a fragmentary cross-sectional view illustrating conditionsjust prior to the closing of the mold with the blow tube in its fullydepressed position;

FIG. 9 is similar to FIG. 8 but with the mold closed onto the blow tube;

FIG. 10 is a view similar to FIGS. 8 and 9 showing the false finish asmolded onto the blow tube after the mold halves have parted subsequentto completion of the blowing cycle;

FIG. 11 is a cross-sectional view on the line XIXI of FIG. 9;

FIG. 12 is a fragmentary cross-sectional view taken approximately on theline XII-XII of FIG. 3 but on a scale reduced somewhat from FIG. 3; and

FIG. 13 is a fragmentary cross-sectional view taken approximately on theline XIIIXIII of FIG. 5 but on a scale reduced somewhat from FIG. 5.

Like characters of reference denote like parts throughout the severalfigures of the drawings. The present invention is concerned primarilywith the extrusion head and with the construction and operation of theextruding members thereof and also with the neck cavity portion of themold means. Accordingly only so much of the surrounding apparatus isillustrated as is proper for a full understanding of the presentinvention.

The several tubular members illustrated in the drawings and described inthe following specification have certain relative vertical movements intimed relation with respect to each other and such movements aredescribed without reference to the means for producing the relativemovements. It will be understood by those skilled in this art that camcontrolled rock arms, fluid pressure cylinders, or other known means maybe employed for producing the required timed axial movements.

Referring particularly to FIGS. 1 and 2, the numeral designatesgenerally an extrusion head proper which comprises a shell or bodymember 21 having a sleeve 22 fixed therein and an end member 23 fixed tothe outer end of shell or body member 21. The removability of sleeve 22and end member 23 from body member 21 facilitates manufacture and thesubstitution of sleeves and end members of various internal diametersand configurations for various jobs, and also facilitates cleaning theplastic flow passages as the necessity arises.

Sleeve member 22 and end member 23 are bored, as shown in FIGS. 1 and 2,to form the external confines of an annular extrusion chamber 25, thebore in the end member 23 being partially tapered as shown, whereby theextrusion chamber reduces in diameter progressively toward its lowerend. The lowermost portion of the extrusion passage 25 is formedexternally by a removable cap 26 which is bored at its upper end to forma continuation of the lower end of the bore of the end member 23 and atits lower end tapers inwardly to form a reduced extrusion orifice 27.

The internal wall of the annular extrusion chamber 25 is formed by anaxially fixed tubular support member 30 and a control sleeve 31 whichtelescopes therein and is generally tapered at its lower end as at 32 togenerally follow the converging tapered portion of the extrusion passagein the cap member 26 as will be described in greater detail laterherein.

A blow tube 33 telescopes within control sleeve 31 and has a relativelyclose sliding fit in the lower end of the control sleeve, as is clearlyshown in FIGS. 1 and 2. In FIGS. 1 and 2 the numeral 34 designates arelatively stationary sleeve having a head member 35 at its lower endwhich closely surrounds blow tube 33 and is tapered externally to form ascraper which prevents upward leakage or passage of plastic materialalong the external surface of blow tube 33.

In FIG. 1 the numerals 37 and 38 designate a pair of mold parts shown inopen position in FIG. 1 but which are closable along a plane through thevertical axis of the extrusion head 20 to form an open-ended mold cavityhaving a main body portion 39, a neck portion 40 and a false finishportion 41. The so-called false finish portion comprises a furtherreduced neck of the molded article which is provided merely for purposesof manufacture and is removed in the course of finishing the outer endof the neck of the molded container.

FIG. 2 is similar to FIG. 1 excepting that it is taken at right anglesthereto and shows a face view of one of the mold halves depicting thecavity portion therein and it will be noted that the wider dimension ofthe body of the finished bottle is as shown in FIG. 2.

FIGS. 3 and 4 show the extrusion orifice portion of the apparatus ofFIGS. 1 and 2 on a greatly enlarged scale. FIGS. 3 and 4 arecross-sectional views taken the same as FIG. 1 but on an enlarged scale.In blow molding flat or non-circular bottles it is desired to extrude atube of plastic material having non-uniform wall thickness around thecircumference in order that more plastic is available for blowing thewider dimension of the body of the bottle.

To this end the beveled lower end 32 of control sleeve 31 is scallopedas shown diagrammatically in the transverse cross-sectional view, FIG.12. In FIGS. 3 and 4 the greater transverse dimension of the beveled end32 of control sleeve 31 is shown in solid lines and the lesser dimension(at right angles to FIGS. 3 and 4) is indicated by dot and dash linesdesignated A in FIGS. 3 and 4.

When blow tube 33 is in the relatively raised position shown in FIG. 3,the wall thickness of the extruded tube is mainly determined by thethickness of the space between the tapered portion of the extrusionorifice and the adjacent beveled end 32 of control sleeve 31.Accordingly, a thinner wall will be produced in the plane of FIGS. 3 and4 than in a plane at right angles thereto.

The reduced end portion 44 of blow tube 33 is not necessarily employedto control or affect the wall thickness of the extrusion and is providedmainly to prevent mushrooming of the plastic emerging from between thebeveled complementary faces of the orifice and the end of control sleeve31.

After the body portion of the tube has been extruded blow tube 33 ismoved downwardly to the position shown in FIG. 4 wherein its largediameter portion lies directly adjacent to the reduced extrusion orifice27 and in this position of the parts the blow tube serves as anextrusion mandrel and the wall thickness of the extrusion is determinedprimarily by the width of the annular space between the periphery ofblow tube 33 and extrusion orifice 27. Thus a uniform wall thicknessportion is extruded to form the neck of the container.

FIG, 5 is a view similar to FIG. 3 but showing an arrangements wherein acontrol sleeve has a beveled end 132 which is a surface of revolutionand wherein the beveled portion of the orifice in cap member 126 isscalloped or formed non-circularly.

In FIG. 5 the numeral designates the beveled surface of the orifice incap member 126 in the plane shown in FIG. 1 for forming the narrowdimension of the body of the bottle, whereas the dot and dash line 151indicates the relative location of the beveled surface of the orifice ina direction at right angles to FIG. 5 for forming the thicker portion ofthat part of the extrusion which forms the body of the bottle. In FIG. 5the numeral 133 designates a blow tube the same as that shown in theembodiment of FIGS. 1 through 4.

Under certain conditions when the blow tube 33 is in the position ofFIG. 4 for final extrusion of a cylindrical neck portion the memoryeffect of the plastic material may result in a non-round extrusion eventhough the final extrusion orifice is truly cylindrical. This memoryeffect is due to the scalloped passage which the plastic traversesbefore reaching the final orifice portion and may occur in either of theembodiments of FIGS. 3 and 4 or FIG. 5. To counteract this tendency itmay on occasion be advisable or necessary to slightly scallop theorifice 27 oppositely to the scalloping of the beveled surfaces 32 or150, as the case may be.

Furthermore, under special circumstances the final extrusion passage maybe non-clyindrical in an opposie direction to that of the control sleeveor the beveled internal surface of the cap member. For instance, it maybe desired to produce a bottle having an oval body and a neck which isoval but in an opposite direction, that is, at ninety degrees to thebody of the bottle. In such case either the final orifice or theextrusion surface of the blow tube may be scalloped accordingly,

FIG. 12 illustrates the non-circularity of the beveled portion 32 ofcontrol sleeve 31, the narrower part extending vertically in FIG. 12 andthe widerpart horizontally. The scalloping of this surface isexaggerated-in FIG. 12 to illustrate the same since the actualdimensional differences in opposite directions are quite small. In FIG.12 the dot and dash line B indicates a true circle, the sides of thebeveled portion 32 being relieved in the manner illustrated in FIG. 12by positioning the part eccentrically in a lathe and cutting fromopposite sides of the bevel 32.

FIG. 13 is an illustration similar to FIG. 12 but illustrating thescalloping of the converging extrusion surface of the member 126 of FIG.5. In FIG. 13 the line C illustrates a true circle, the tapered surfacebeing given greater width vertically than horizontally, again bypositioning the part eccentrically in a lathe and taking cuts fromopposite sides of the beveled surface. Whereas the foregoingcontemplates scalloping of either the ex trusion orifice or the controlsleeve, under some circumstances scallop formations may be formed onboth the external and internal extrusion members.

As indicated in the preamble hereto, difiiculty is ordinarilyencountered in properly molding a false finish between the false finishportion of the cavity in the mold members and the peripheryof blow tube33. It is impractical to extrude a tube of precise wall thickness, Ifthe wall is too thin there is not enough plastic to fully mold the falsefinish which leaves a partial void in the molded false finish. If thewall thickness of the extrusion is too thick it causes a harmful flashof fin which prevents the mold parts from closing properly andinterferes with subsequent machine handling and other treatment of thebottles, including difficulty in trimming thereof.

The present apparatus solves this problem by deliberately molding finsof controlled maximum dimension along the (false finish. The specialcavity portions provided for molding the fins need not be filled withplastic material upon closure of the mold and thus they provide a spacefor variable amounts of excess plastic. Accordingly, the extrusionportion which forms the false finish may be made thicker than the actualprecise thickness required to completely mold the false finish, suchexcess thickness being variable within certain limits to providereasonable manufacturing tolerance.

The cavity portions thus provided for molding fins along the sides ofthe false finish of the bottle may be partly in each half of the moldbut in the present instance involve only one-half of the mold, namelythat half designated 37 in FIGS. 1 and 2. Referring to FIGS. 6 and 7,the semicircular tfalse finish cavity 41 in mold half 37 has a marginalsurface portion 175 which is set back slightly from the normal surfaceof the mold half, that is the plane of parting of the mold halves.

Adjacent to this set-back surface 175 at each side of cavity 41 is afurther set-back or recess portion 176 which is deeper than the set back175. The cross-sectional configuration produced by the set-back surfaces175 and 176 is shown in FIG. 11 and as a result of this recessarrangement excess plastic resulting when the mold halves close to moldthe false finish portion produces fins having attenuated portionsadjacent to the false finish itself, as clearly shown in FIGS. 10 and11. In FIGS. 10 and 11 the thin portions of the fins are designated 178and the thicker outer parts are designated 17 9.

Advantage of this form of fin resides in the fact that the thin partpinches the plastic to prevent escape of air while the thick partprovides substantial space for excess plastic. While the form of finsshown herein is advantageous for the foregoing reason, other forms ofdeliberately molded fins may be employed for the same general purpose ofinsuring a fully molded false finish while also assuring that the moldparts will not be prevented from closing.

Groove formations 181 in the false finish mold cavity portions 41 form abead on the false finish as indicated at 182 in FIG. 10. These beadformations are for use in subsequent handling of the articles and arenot germane to the present invention.

I claim:

1. Apparatus for extruding plastic material in tubular form comprisingan extrusion chamber terminating in a reduced extrusion orifice, saidchamber having a wall portion converging to and merging with saidorifice by means of a continuous streamlined surface, a first mandrelmember disposed coaxially in said chamber and having a cylindrical outerperipheral portion, a second mandrel member comprising a hollowcylindrical member having its internal bore portion slidable on theouter cylindrical portion of the first mandrel member, the outer endsurface of said second mandrel member being generally complementary tothe continuous streamlined surface of said converging chamber wallportion and merging with the cylindrical portion of said first mandrelmember, said surfaces defining a first annular extrusion passage ofgreater effective thickness at certain points about its circumferencethan at others and said second mandrel member being axially movableduring extrusion, whereby a tubular extrusion of non-uniform wallthickness both circumferentially and in an axial direction may beformed, said first mandrel member having an end portion disposed in saidreduced extrusion orifice to define a second annular extrusion passagewhich comprises a continuation of the first annular extrusion passage,the axial movement of said second mandrel member determining therelative effectiveness of said first annular extrusion passage and saidsecond annular extrusion passage in defining the Wall thickness andcircumferential distribution of plastic material in said extrusion.

2. Apparatus according to claim 1 wherein said converging wall portionis a surface of revolution.

3. Apparatus according to claim 1 wherein the outer end surface of saidsecond mandrel member is a surface of revolution.

4. Apparatus according to claim 1 wherein said reduced extrusion orificeis a surface of revolution.

5. Apparatus according to claim 1 wherein said first mandrel end portionis a surface of revolution.

6. Apparatus according to claim 1 wherein said first mandrel is axiallymovable relative to said reduced extrusion orifice.

7. Apparatus according to claim 1 including blow mold means incombination therewith and in which said first mandrel comprises a blowtube.

References Cited UNITED STATES PATENTS 3,078,507 2/1962 Park 185 X I.SPENCER OVERHOLSER, Primary Examiner. W. L. MCBAY, Assistant Examiner.

1. APPARATUS FOR EXTRUDING PLASTIC MATERIAL IN TUBULAR FORM COMPRISINGAN EXTRUSION CHAMBER TERMINATING IN A REDUCED EXTRUSION ORIFICE, SAIDCHAMBER HAVING A WALL PORTION CONVERGING TO AND MERGING WITH SAIDORIFICE BY MEANS OF A CONTINUOUS STREAMLINED SURFACE, A FIRST MANDRELMEMBER DISPOSED COAXIALLY IN SAID CHAMBER AND HAVING A CYLINDRICAL OUTERPERIPHERAL PORTION, A SECOND MANDREL MEMBER COMPRISING A HOLLOWCYLINDRICAL MEMBER HAVING ITS INTERNAL BORE PORTION SLIDABLE ON THEOUTER CYLINDRICAL PORTION OF THE FIRST MANDREL MEMBER, THE OUTER ENDSURFACE OF SAID SECOND MANDREL MEMBER BEING GENERALLY COMPLEMENTARY TOTHE CONTINOUS STREAMLINED SURFACE OF SAID CONVERGING CHAMBER WALLPORTION AND MERGING WITH THE CYLINDRICAL PORTION OF SAID FIRST MANDRELMEMBER, SAID SURFACES DEFINING A FIRST ANNULAR EXTRUSION PASSAGE OFGREATER EFFECTIVE THICKNESS AT CERTAIN POINTS ABOUT ITS CIRCUM-